Wankel, Your confusion may be that a car may run faster on a power supply with lower voltage, but higher amperage, because the stock power supplies do not supply as much amperage as the cars will draw at full throttle, even though they have relatively high voltage. This is especially true for magnet cars which put a higher load on the motor. The amp draw is directly proportional to the load on the motor. When breaking in motors, they are usually run with no load, so they will not draw much amperage at all and the rpm is dictated by voltage. Hope this makes some sense.